Mobile radio antenna



July 14, 1959v l. KAMr-:N ETAL MOBILE RADIO 'ANTENNA Filed Jan. 30, 1956AVC United States Patent() MOBILE RADIO ANTENNA Ira Kamen, New York, andSalvatore P. Angelastro,

Brooklyn, N.Y., assignors to General Bronze Corporation, Garden City,N.Y., a corporation of New York Application January 30, 1956, Serial No.562,077

`6 Claims. (Cl. 343-717) This invention relates to antennas for mobileradio receivers and particularly concerns an automobile antenna ofsubstantially omni-directional characteristics.

Heretofore the type lof automotive radio antenna in most common use hasbeen the metal whip, which is formed of stify resilient tubing in aplurality of telescoping sections, vertically oriented and extensible toa length of three or four feet. The Q of such an antenna is limited bythe quality of the insulation in its supporting bases and in the coaxialtransmission line which is used to connect them to the input of theautomobile radio receiver.

In the radio receiver, the input circuit has conventionally been tunedby a variable powdered iron core inductor forming part of a parallelresonant circuit. Such inductors necessarily have a low Q because of thepresence of the chassis of the radio receiver and other adjacentmetallic structures. As a practical matter, it has been impossible toachieve Q values of an order substantially exceeding l0, and the low Qof the antenna circuitry has seriously limited the overall gain of thereceiving system.

Whip-type antennas have been generally lregarded as detracting from theaesthetic appearance of the automobile. Moreover, they have often beendamaged by collision with garage doors, trees and other objects, and

their telescoping action, if not their electrical efiicacy, has beenimpaired.

In our copending application Serial No. 533,939, tiled September 13,1955, now abandoned, there is disclosed a magnetic antenna comprising acore of high-permeability, high-Q magnetic material with a coil of wirewound helically around it, the coil being connected in parallel with acondenser in the input circuit of the radio receiver to form a circuitresonant at the frequencies to be received. Thus, the antenna coil hasserved not only as a pick-up device but also as part of the tuned inputcircuit ofthe receiver. This has eliminated the necessity of an inputinductance within the receiver and has made it pos- ,sible to achieve Qvalues of the order of a hundred or more.

Despite the small physical size and resulting unobtrusiveness of theantenna disclosed in the aforen1en tioned co-pending application SerialNo. 533,939, it has an average gain comparable to or superior to that ofa conventional, fully extended metal whip. However, the antenna is mostecient when mounted in the horizontal plane so that the long axis of thecore is parallel to the H or magnetic component of a verticallypolarized broadcast signal. When the antenna is so oriented, it exhibitsa definite directional characteristic, the pick-up of the antenna beingmaximum when the long axis of the core is oriented parallel to the wavefront of the broadcast signal-ie., broadside to the direction from whichthe signal emanates. While the automatic volume control action of aconventional automobile radio receiver is suiicient to overcome thisundesirable directional characteristic to a large extent, thesensitivity of the antenna, when` unfavorably oriented, is somethingless than that of a fully extended whip. In poor receiving locations,

2,895,129 Patented July 14, 1959 for example locations at a considerabledistance from the transmitting station in what is sometimes termedfringe areas, the directional effect of the antenna is therefore quitenoticeable to the listener as the automobile is turned.

It is therefore among the objects of the present invention to provide amagnetic type automobile radio receiving antenna which is substantiallyomni-directional in its characteristics. Another object of the inventionis t0 provide such an antenna which is sufliciently sensitive to permitit to be mounted beneath the automobile or in other inconspicuouslocations where the eld intensity is low. A yfurther object of theinvention is that of providing such an antenna which is practical andeconomical in construction and which is well adapted for conditions ofactual use. A still further object is that of providing such an antennawhich includes means for varying its inductance and thereby changing theresonant frequency of the tuned circuit in which it is incorporated.

In the drawings:

Figure 1 is a top plan view of an antenna embodying features of theinvention, with portions of the antenna being shown in section to revealits inner construction.

Figure 2 is a schematic diagram of the input circuit of a radio receiverincluding the antenna of Figure l.

Figure 3 is a somewhat diagrammatic perspective view, partly brokenaway, of an alternative embodiment of this invention which includesmeans for varying the inductance of the antenna.

As may be seen in Figure 1, the antenna includes a helical coil 10 whichis wound on an elongated cylindrical core 12 of a high-permeability,high-Q magnetic material such as a ferrite of the type sold by Henry L.Crowley and Co. under the designation Croloy (2R-20 or by GeneralCeramics Corporation under the designation Ferramic Q. In the particularembodiment illustrated, the core 12 is approximately 15 inches inoverall length and 5/8 inch in outside diameter; it is tubular in formhaving a hollow axial bore approximately 1A inch in diameter. The coil10 comprises approximately 47 turns of No. 28 A.W.G. double silk coveredwire which is wound directly on the core and spaced so as to occupysubstantially the full length of the core.

The core 12 is supported at its ends in slots in a housing 14-which, forexample, is molded of a therm'osettng phenolic resin. The housing 14vCompletely encloses the core 12 and coil 10 and protects them fromphysical damage as well as from dirt and moisture.

The housing 14 is secured by means of screws 16 on a plate 18. The plate18 is suitably formed 'of aluminum 7" x 17" x 1/32, although thesedimensions are not at all critical. The core 12 and coil 10 aresupported so that the axis of the core 12 is parallel to the plate 18,with a spacing of approximately 1%," between the plate and the adjacentside on the core. The plate 18 is provided at its four corners withmounting straps 20, of a suitable insulating material such aspolystyrene, which are used to secure the plate 18 and the attachedhousing 14 in position beneaththe automobile body.

Electrical connection is made to the antenna through a conventionalcoaxial transmission line 22, the terminal tting 24 lof which cooperateswith a complementary fitting 26 secured to the housing 14. The centerconductor 28 of the coaxial line 22 is connected through the ittings 24and 26 with one terminal 30 of the coil 10, and also to the plate 18through one of the screws 16. The outer braid 32 of the coaxial line 22is connected through a lead 34 with the opposite terminal 36 of the coil10.

Figure 2 is a schematic electrical diagram of an illustrative circuit bywhich the antenna may be connected to the input of an automobile radioreceiver. As may be Seen in this figure, the plate 18 andthe terminal 30of the coil 10 are connected through the central conductor 28 of thetransmission line and through a coupling capacitor 37 to the grid of theinput tube 38 of the automobile radio receiver. The other terminal36 ofthe coil 10 is connected through the outer braid 32 of the coaxial lineto thev grounded chassis of the radio receiver.

Mounted within the radio receiver and connected Ybetween the centralconductor 38 and ground and thus in parallel with the coil 10, is avariable tuning condenser V40 witha padding condenser 42 connected inparallel with it for tracking purposes. The effective capacitance of thecircuit includes not only the lumped capacitances of the tuningcondenser 40 and padder 42, but also the distributed capacitance of thecircuit including the capacitance between the plate 18 and ground, asindicated in broken lines at 44, the `distributed capacitance of thecoil 10, as indicated in broken lines at 46, and the capacitance of thecoaxial transmission line as indicated in broken lines at 48. All ofthese capacitances, of course, must be taken in consideration indetermining the proper value of inductance of the coil 10 andcapacitance of the condensers 40 and 42. It has been found thata tuningcondenser 40 having a capacitance range of 14 to 540 mmf. will properlytune the broadcast band with a plate and coil of the characteristicshereinabove described.

From a study of the circuit of Figure 2, it can be seen that the coil 10and capacitance 40, in combination with the padder 42 and thedistributed capacitances 44, 46 and 48, form a parallel circuit which isresonant at the frequencies to be received. Since the coil 10 is mountedexternally of the radio receiver and is inherently a high Q device, itis possible to achieve Qs of the order of 1G() or more. This gives thecircuit a high EQ product and an excellent signal sensitivity.

The antenna unit, as illustrated in Figure l, is preferably mounted withthe plate 18 in a horizontal plane. This orients the long axis of thecore 12 broadside parallel to the H or magnetic plane of a verticallypolarized signal. Where the long axis of the core 12 is orientedbroadside to the direction from which the received signal emanates, thepickup of the coil 10 is at a maximum and the sensitivity of the antennais many times greater than Athat of a conventional fully extended whip.The amplitude of signal pickup by the coil 10 falls off where the longaxis of the core 12 is oriented parallel to the direction from which thereceived signal emanates. However, the plate 18 serves as a pickupdevice which is substantially omnidirectional, and the signal picked upyby it is always additive to that induced in the coil 10. Thus, even atthe most unfavorable orientation of the antenna, its overall sensitivityis markedly Vsuperior to that of a fully extended whip. While the 'lieldSensitivity pattern of the antenna is not uniform in all directions, inits poorest orientation, it is better than a fully extended whip. Thevariation in signal pickup as the automobile is turned will usually bewithin the range of compensation of the receivers automatic volumecontrol, so that no variation in signal volume is observed by thelistener as the car is turned.

The sensitivity of the antenna is sufficient that it may even be mountedbeneath the automobile. When so mounted, it is preferably oriented sothat the housing y14 is on the upper side of the plate 18. As oneexample "located with the long axis of the plate 18 aligned with thelong axis of the car, with the leading edge of the *plate spacedapproximately l inches 'rearwardly of the center post of the car (afour-door sedan), and with the left-hand edge of the plate 18 spacedapproximately 9 inches inwardly from the adjacent left-hand edge of thecar body. i

The antenna as thus mounted is entirely inconspicuous and does notinterfere `with the streamlining of the car. ItS sensitivity is so greatthat even though mounted beneath the car it gives superior performanceas compared to a conventional fully extended whip in all orientations ofthe automobile relative to the direction of the received signal.

Figure 3 illustrates an alternative embodiment of the invention whichincludes means for varying the inductance of the coil. As may be seen inthis ligure, the coil 56 is wound on a tubular core 58 which hasslidably received in one end thereof an auxiliary core 60 ofcomparatively small diameter. By moving the auxiliary core 60 inwardly(toward the left as viewed in Figure 3) so that more of its length isreceived with-in the bore 58a of' the main core 58, the inductance ofthe coil 56 may be increased, and vice versa, This feature ofvaria-bility, in combination with the paddling condenser 42, allowstracking of the input circuit so that the tuning condenser 40 may beganged for simultaneous tuning with one or more additional condensersections connected in various circuits within the receiver.

From the foregoing description, i-t will be understood that the presentinvention provides an antenna which is simple and economical inconstruction and which is substantially omnidirectional in itscharacteristics, and which is suiiciently sensitive -to permit it to bemounted underneath the automobile or -in some other inconspicuouslocation. It will therefore be appreciated that the aforementioned andother desirable objectives have been achieved. However, it should beemphasized that the particular vembodiments of the invention which aredescribed and shown herein are intended as merely illustrative ratherthan as restrictive of the invention. i

We claim:

1. A mobile radio antenna comprising a metallic sheet member, means forsupporting said sheet member in electrically insulated relation to avehicle, an elongated core of high-permeability, high-Q magneticmaterial, means for supporting said core in a generally horizontal planeand in spaced relation to said vehicle, a coil wound on said core, andmeans for electrically connecting said coil and said sheet to the inputcircuit of a radio receiver in said vehicle.

2. An automobile radio antenna comprising a metallic sheet member, meansfor supporting said sheet member in a` generally horizontal plane-beneath the body of an automobile and in electrically insulatedrelation thereto, an elongated core of high-permeability, high-Qmagnetic material, means for supporting said core in a generallyhorizontal plane beneath said automobile body and in electricallyinsulated relation thereto, a coil wound on said core, and means forelectrically connecting said coil and said sheet to the input circuit ofa radio receiver in said vehicle.

3. An automobile radio antenna comprising a metallic sheet member, meansfor supporting said sheet member ina generally horizontal plane beneaththe `body of an automobile and in electrically insulated relationthereto, an elongated core of high-permeability, high-Q magneticmaterial, means for supporting said core in a generally horizontal planeon top of said sheet member and in spaced, generally parallel relationthereto, a helical coil wound on said core, and means for electricallyconnecting said coil and said sheet to the input circuit of a radioreceiver in said vehicle.

4. A mobile radio antenna comprising a metallic sheet member, means forsupporting said sheet member in electrically insulated relation to avehicle, an elongated core of high-permeability, high-Q magneticmaterial, means for supportingsaid core in a `generally horizontal planeand in spaced relation to said Vehicle, a coil wound on said core, meansconnecting said metallic sheet member to one end of said coil, and meansto connect said coil across a variable condenser in the input circuit ofa radio receiver in said vehicle to form with said condenser and thedistributed capacitance of the circuit a tuned circuit resonant at thefrequencies to be received.

5. An automobile radio antenna comprising a metallic sheet member, meansfor supporting said sheet member in a lgenerally horizontal planebeneath the body of an automobile and in. electrically insulatedrelation thereto, an elongated core of high-permeability, high-Qmagnetic material, means for supporting said core in a generallyhorizontal plane on top of said sheet member and in spaced, generallyparallel relation thereto, a helical coil wound on said core, and acoaxial transmission line, one end of the inner conductor of saidtransmission line being connected to one end of said coil and to saidmetallic sheet member, and the other end of said inner conductor beingconnected to one set of plates of a variable condenser in the inputcircuit of a radio receiver and one end of the outer braid of saidcoaxial transmission line being connected to the other end of said coiland being lgrounded to said automobile body and the other end of saidouter braid being connected to the other set of plates of said condenserto form a parallel tuned circuit resonant at the frequencies to tbereceived.

6. A mobile radio antenna comprising a metallic sheet member, means forsupporting said sheet member in electrically insulated relation to avehicle, a core assembly including a main core of high-permeabilityhigh-Q magnetic material and an auxiliary core of similar materialmounted adjacent said main core and movable relative thereto to Vary theeffective overall size of said core assembly, means for supporting saidcores in spaced relation to said Vehicle, a coil Wound on said maincore, and means for electrically connecting said coil and said sheet tothe input circuit of a radio receiver in said vehicle.

References Cited in the tile of this patent UNITED STATES PATENTS2,055,830 Vincent Sept. 29, 1936 2,335,969 Schaper Dec. 7, 19432,740,113 Hemphill Mar. 27, 1956 2,750,497 Stott lune 12, 1956 2,755,468Mountjoy July 17, 1956

